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comparison lemuriformes/cast.py @ 5:dbbf5344868c

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add utlities for casting data
author Jeff Hammel <k0scist@gmail.com>
date Sun, 10 Dec 2017 11:51:39 -0800
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4:9575c4a925c1 5:dbbf5344868c
1 """
2 methods for casting data
3 """
4
5 import datetime
6 from collections import OrderedDict
7
8
9 try:
10 # python2
11 string = (str, unicode)
12 except NameError:
13 # python3
14 string = (str,)
15
16 def isstring(f):
17 return isinstance(f, string)
18
19 # types we expect to encounter
20 types = OrderedDict([('int', int),
21 ('float', float),
22 ('str', str)])
23
24
25 def keyvalue(_string, separator='='):
26 """
27 cast `_string` to [`key`, `value`] split on `separator`
28 """
29
30 if separator not in _string:
31 raise AssertionError("Separator '{}' not in '{}'".format(separator,
32 _string))
33 return _string.split(separator, 1)
34
35
36 def string_to_bool(string):
37 """cast a string to a `bool`"""
38 return {'true': True,
39 'false': False}.get(string.lower())
40
41
42 def unify(item, codec='utf-8'):
43 """cast item to unicode carefully if a string; otherwise, return it"""
44
45 if not isinstance(item, string):
46 return item
47 return item.encode(codec, 'ignore')
48
49
50 def datetime_handler(x):
51 """handler for JSON serialization"""
52
53 # Ref
54 # https://stackoverflow.com/questions/35869985/datetime-datetime-is-not-json-serializable
55 if isinstance(x, datetime.datetime):
56 return x.isoformat()
57
58 # go through the normal types for type casting
59 # (and hope nothing "weird" happens")
60 for _type in types.values():
61 try:
62 return str(_type(x))
63 except ValueError:
64 continue
65
66 # worst case scenario
67 raise TypeError("Unknown type: {x}".format(x=x))
68
69
70 def isiterable(obj):
71 """determines if `obj` is iterable"""
72
73 try:
74 iter(obj)
75 return True
76 except TypeError:
77 return False
78
79
80 def iterable(obj):
81 """make an iterable out of `obj`"""
82 return obj if isiterable(obj) else (obj,)
83
84
85 def infer(strings, types=types.values()):
86 """
87 inferrred the type of a bunch of strings
88 """
89 for _type in types:
90 for s in strings:
91 try:
92 _type(s)
93 except ValueError:
94 break
95 else:
96 return _type
97
98
99 def cast(strings, types=types.values()):
100 """
101 cast `strings` to `types` based on inference
102 """
103
104 _type = infer(strings, types=types)
105 return [_type(s) for s in strings]